Home / Statistical Tools / Control Charts / Individuals
Individuals¶
From Excel click...
QXL Stat Tools Tab > Control Charts > Variables > Charts as Individuals > Individuals
Want to build one first?
The walkthroughs live with the full chart: How-To builds one step by step from sample data you copy off the page straight into Excel, and How-To with GroupBy does the same with a grouping column. Both draw both panels; switch the Chart: radio group to this variant at the same point in the steps to follow along here.
An Individuals chart is one panel, Individuals Chart, built from measurements taken one at a time. Every observation is plotted as its own point, with a center line at the mean of the observations and a control band either side of it. It is the upper panel of an I-MR chart drawn on its own, without the moving range panel below it.
The ribbon entry is Individuals, but the dialog it opens is titled I-MR Chart, because one dialog serves the I-MR, Individuals, and Moving Range entries and its title follows the family rather than the variant. Only the worksheet differs: the sheet this variant writes is named Individuals Chart. Every option in that dialog is described on the Options page.
When to use it¶
- Your measurements are continuous, and the process gives you one measurement per point in time: one reading per batch, one part per hour, one result per test run.
- There are no subgroups to form. This dialog has no Subgroups group at all, so each selected row is one plotted point and there is no subgroup size to set.
- You want the individual values on their own, with no moving range panel underneath. If you want both panels, use the I-MR entry; if you want the lower panel on its own, use Moving Range.
If the process gives you two or more measurements per point in time, use an Xbar-R or an Xbar-S chart instead.
How it works¶
Quantum XL plots each selected row as one point, in worksheet order. The center line is the mean of the observations.
The limits come from a single within sigma estimated once for the whole chart (once per phase when the chart is split). This variant selects Square root of MSSD for you, which builds the estimate from the squared differences between consecutive observations. Average moving range and Median moving range are also offered, and both build the estimate from moving ranges instead. The limits sit a number of estimated standard deviations either side of the center line, and because every point carries one observation they are straight lines rather than the stepped limits of a subgrouped chart.
Selecting this variant changes the sigma method for you. The dialog silently switches to Square root of MSSD when you select Individuals, and silently switches back to Average moving range when you leave it, though only if Square root of MSSD is still the selected method at that point. Choosing Square root of MSSD also clears the Nelson moving-range correction and hides the Moving range length: box. None of the three is announced. The Options page describes all of them.
The moving range panel is still computed even though it is not drawn, so the whole dialog, including its moving range settings, behaves exactly as it does on an I-MR chart.
Two settings change what the limits describe rather than how they are computed. Estimate Limits From computes the limits from the first few points only and extends them across the whole chart. Split Control Limits divides the chart into phases, each with its own center line and limits.
The exact formulas are on the Math Details page.
Output¶
The analysis writes one worksheet named Individuals Chart. Under GroupBy there is one worksheet per group, each named Individuals Chart - {GroupName}.
Worksheets are divided by GroupBy group, not by chart. Every chart belonging to a group is stacked down that one worksheet, one below the other, so selecting three measurement columns without GroupBy produces three charts on a single sheet rather than three sheets. The User Input block is written once at the top of each worksheet; everything after it repeats for each chart on the sheet.
On the sheet, from the top:
- A User Input block in the first two columns, holding the analysis title, the columns you selected, and whether the calculation type was Excel or GroupBy. Modify Existing Analysis reads it back.
- The Individuals Chart panel, plotting each observation with its center line and control limits, plus the zone lines, reference lines, and phase dividers if you asked for them. Points that broke an enabled out-of-control test are drawn in a different color.
- A summary table to the right, listing the center line, the control limits where they exist, the count of out-of-control points, and the count of points you marked as outliers. A transformation adds rows naming the type and its parameters; a split chart adds a per-phase breakdown.
- A capability and histogram block below the panel, but only when you entered a specification limit or a target on the Capability tab.
When the analysis finishes, the Control Chart task pane opens on the right. See Task Pane for what it can and cannot change.